Different types of filter bed reactors for purifying or refining a fluid or liquid are known in the art. In the conventional stationary filters, solids are progressively accumulated in the filter bed, increasing the head loss until the filter material must be cleaned by backwashing before treatment can resume. The times between backwashings can vary, and if these times are too short, the effective operating time of the system can be considerably reduced.
In continuous bed filter reactors, the fluid to be purified is conducted through the filter bed and the filter material is brought to motion by means of a transport system. Bringing to motion the filter material is often done by making the filter material circulate through the filter bed, for example by bringing the filter material from the bottom of the filter bed to the top where it is deposited, either before or after the filter material is treated, and letting it drop again to the filter bed, so that it can continuously keep moving from the bottom to the top. These are in general auto-refining systems, wherein the eliminated parts are continuously drained in a concentrated stream.
This type of continuous bed filter reactors are increasingly being used for the refinement of industrial and domestic waste water, and for the purification of drinking water.
EP 730 895 A1 discloses a typical prior art sand filter, comprising a cylindrical vessel with an oblique conical bottom along which the filter material of the filter bed slides down before it is lifted with an air lift for purification. Water to be cleaned is generally introduced in an inlet in the top half of the vessel. These apparatuses have the disadvantage, due to the conical bottom, of being normally quite high, around 6 to 7 meters. This can make construction more complicated and expensive. Furthermore, the filter bed is often unevenly loaded and, as a consequence, preferred fluid paths might be created, especially as the diameter of the filter is bigger. For both reasons, the diameter of this type of filters is normally limited to a maximum of 4 meters.